As is known, sensing elements are used in a variety of applications to sense characteristics of an environment. Sensing elements include, but are not limited to, pressure sensing elements, temperature sensing elements, light sensing elements, acoustic sensing elements, and magnetic field sensing elements.
A magnetic field sensor can include one or more magnetic field sensing elements and also other electronics.
Magnetic field sensors can be used in a variety of applications. In one application, a magnetic field sensor can be used to detect a direction of a magnetic field. In another application, a magnetic field sensor can be used to sense an electrical current. One type of current sensor uses a Hall effect magnetic field sensing element in proximity to a current-carrying conductor.
Planar Hall elements and vertical Hall elements are known types of magnetic field sensing elements that can be used in magnetic field sensors. A planar Hall element tends to be responsive to magnetic field perpendicular to a surface of a substrate on which the planar Hall element is formed. A vertical Hall element tends to be responsive to magnetic field parallel to a surface of a substrate on which the vertical Hall element is formed.
Other types of magnetic field sensing elements are known. For example, a so-called “circular vertical Hall” (CVH) sensing element, which includes a plurality of vertical magnetic field sensing elements, is known and described in PCT Patent Application No. PCT/EP2008/056517, entitled “Magnetic Field Sensor for Measuring Direction of a Magnetic Field in a Plane,” filed May 28, 2008, and published in the English language as PCT Publication No. WO 2008/145662, which application and publication thereof are incorporated by reference herein in their entirety. The CVH sensing element is a circular arrangement of vertical Hall elements arranged over a common circular implant region in a substrate. The CVH sensing element can be used to sense a direction (and optionally a strength) of a magnetic field in a plane of the substrate.
Conventionally, all of the output signals from the plurality of vertical Hall elements within the CVH sensing element are needed in order to determine a direction of a magnetic field. Also conventionally, output signals from the vertical Hall elements of a CVH sensing element are generated sequentially.
Various parameters characterize the performance of sensing elements (and sensors that use sensing elements) in general, and magnetic field sensing elements (and magnetic field sensors) in particular. Taking a magnetic field sensing element as an example, these parameters include sensitivity, which is a change in an output signal of a magnetic field sensing element in response to a change of magnetic field experienced by the magnetic sensing element, and linearity, which is a degree to which the output signal of the magnetic field sensing element varies in direct proportion to the magnetic field. These parameters also include an offset, which is characterized by an output signal from the magnetic field sensing element not representative of a zero magnetic field when the magnetic field sensing element experiences a zero magnetic field. Other types of sensing elements can also have an offset of a respective output signal that is not representative of a zero sensed characteristic when the sensing element experiences the zero sensed characteristic.
Another parameter that can characterize the performance of a magnetic field sensing element is the speed with which output signals from the magnetic field sensing elements can be sampled.
The CVH sensing element is a moderately complex structure formed upon a substrate. It would be desirable to be able to self-test the CVH sensing element. One form of self-test can identify if the plurality of output signals from the CVH sensing element operating in normal operation are correct when the CVH sensing element is in the presence of a magnetic field.
This type of self-test could be performed during manufacturing. However, when in use in the field, the direction and strength of an external magnetic field used to test the CVH sensing element are difficult to control, and thus, the self-test using the external magnetic field would be of limited use.
The same limitations apply to a self-test of a magnetic field sensor that uses the CVH sensing element.
Thus, it would be desirable to have a form of self-test of a CVH sensing element and/or a self-test of a magnetic field sensor that uses a CVH sensing element, wherein the self-test does not depend upon a magnetic field.